Use ERT with multicol.
See the "Multiple Columns" section in Extended.lyx
Baically, put \usepackage{multicol} in the preamble, then do a \begin{multicols}{2} right when you want the 2-column to be (right after the abstract) and do \end{multicols} where you want it to end.
in the default twocolumn mode you can have floats, with the multicol package not.
Herbert
